RA is a chronic inflammatory disease of the entire body wherein hyperplasia is seen in the synovial tissue of joints. Synovial cells are fibroblastoid cells that form the one to six epithelioid layers of the synovial membranes of joints, and are thought to supply proteoglycan and hyaluronic acid to the synovial fluid. Hyperplasia of the synovial tissue is seen in the joints of RA patients along with the resulting symptoms of multilayer structures and infiltration of synovial cells into other tissue caused thereby. In addition, the blood serum of an RA patient contains autoantibodies to the Fc domain of its own IgG. Accordingly, this is thought to be an autoimmune disease, but its cause has yet to be elucidated.
The aforementioned presence of autoantibodies that recognize self-IgG has been long utilized as a characteristic diagnostic indicator of RA. Autoantibody detection kits containing modified human IgG as the main component have recently become commercially available. This autoantibody is also called the RA factor. The diagnosis of RA based on the detection of the RA factor has problems with respect to specificity to the disease and that the relationship to the cause is unclear since the system by which antibodies occur has not been elucidated.
When the pathology of RA is examined from the two aspects of that of the various immune reactions in the body and that of a hyperplastic disease of the joint synovial membrane accompanying bone disruption, much research has been performed regarding the former immune reactions and the molecular mechanism thereof is about to be clarified. However, regarding study of the latter joint synovial cells, even though this is a principal aspect of RA, even their cytobiological characteristics have to be clarified at present. Elucidating the molecular mechanism behind the onset and progress of RA and other chronic and intractable diseases is indispensable for the diagnosis, prevention and cure of the diseases. Moreover, in the current situation in which the aging of society does not show signs of halting, elucidating the pathology of the aging disease RA is an important problem from a societal standpoint also.